Cell Biology and Life Processes
What this domain tests
Cell Biology and Life Processes tests cell structure, microscopy, transport across membranes, enzymes, photosynthesis, respiration and cell division.
Core rules
- Animal cells have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a cell wall, chloroplasts and a large vacuole.
- The nucleus controls activities and holds DNA; mitochondria release energy by respiration; ribosomes make proteins; chloroplasts carry out photosynthesis.
- Diffusion moves particles from high to low concentration. Osmosis moves water across a partially permeable membrane from a dilute to a concentrated solution. Active transport needs energy.
- Enzymes are biological catalysts with an optimum temperature and pH; they are denatured above the optimum.
- Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ using light and chlorophyll.
- Aerobic respiration: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy.
- Mitosis produces genetically identical cells for growth and repair.
Worked example
A plant cell is placed in pure water. The water potential outside is higher than inside, so water enters by osmosis. The vacuole swells and the cell becomes turgid; the cell wall prevents bursting. In concentrated salt solution, water leaves and the cell becomes plasmolysed.
Traps
Do not confuse respiration with photosynthesis; respiration occurs all the time. Do not say enzymes are 'killed' by heat; they are denatured. Osmosis refers to water, not any solute. Plant cells do not burst because of the cell wall.